Marking instruments in the form of crayons have been used by young and old for decades. Historically, crayons have been manufactured by mixing together a binder, the binder typically constituting a molten wax, and a suitable pigment. The molten mixture would then be extruded into a desired shape, e.g., a cylinder, and subsequently cooled to effect solidification of the mixture. The resulting crayon, when rubbed on a surface, such as paper, would leave a mark, i.e., a residue of pigmented wax, on the paper's surface.
Over the years, the crayon has undergone a number of changes to improve its appearance, mechanical properties, and marking properties, as well as its toxicity. One of these changes, which affects at least the appearance of the crayon, is that relating to pigments. The introduction of new pigments over the years has provided crayon developers with the ability to produce crayons having a variety of vivid and attractive colors. This increase in the availability of colors and hues in crayons has fueled the demand for further improvements in the properties of crayons, generally. One of the areas of crayon development which has been affected by the foregoing may be characterized as the area of "special effects."
One of these special effects is phosphorescence. Phosphorescence is achieved by the use of phosphors, which are substances which emit light when excited by radiation. Phosphors have been known for years, and have been incorporated into different types of marking compositions. By way of example, a phosphorescent marking composition in the form of a crayon, pencil or chalk was described and patented in 1882 (Horne, U.S. Pat. No. 257,706). This marking device, however, is relatively unsophisticated, being comprised of a phosphorescent substance, pipe clay, curd soap, gum arabic, and water. A more recent example of a phosphorescent marking material, which comprises a wax base vehicle, filler particles, and phosphorescent particles, is described in U.S. Pat. No. 5,116,533.
Another aspect of the special effect area is fluorescence. This property is obtained by the use of fluorescers, which are substances which emit electromagnetic radiation (usually as visible light) resulting from (and occurring only during) the absorption of radiation from some other source. Examples of pigments which fluoresce under daylight conditions are described in U.S. Pat. No. 3,939,093. Such fluorescent pigments have also been included in marking compositions, e.g., U.S. Pat. No. 3,057,806, which describes fluorescent crayons.
One U.S. patent which discloses pigment compositions which comprise a combination of common pigments, phosphorescent pigments, and fluorescent pigments, is U.S. Pat. No. 4,725,316. These pigment compositions are said to be combinable with translucent plastics, resins, and natural and synthetic rubbers. However, there is no mention of their use in connection with crayons.
Another area of crayon technology which has undergone significant change over the years is the composition of the binder component. The natural waxes, which were historically used as binders, have been improved through blending and the inclusion of additives. In addition, synthetic materials have been developed which provide, among other advantages, a more uniform distribution of pigment throughout the crayon, and the ability to successfully mark a relatively wider variety of surfaces.
One patent which is exemplary of those in which synthetic binders are included in a crayon composition is U.S. Pat. No. 4,978,390. The compositions disclosed therein comprise, generally, polyethylene glycols, a pigment, certain other alcohols, and other components. This patent specifically states, however, that only certain polyethylene glycol binders be used in the composition--those having a molecular weight of above 7,000. Polyethylene glycols having a molecular weight below 7,000 should be avoided, according to the patent.
The formulation of any marking composition which is intended to be used in the form of a crayon should further be developed so that the crayon provided thereby possesses good appearance, good mechanical and marking properties, and relatively low toxicity. More particularly, a crayon should advantageously possess sufficient mechanical strength so it can successfully withstand rubbing on a surface without undue crumbling or breaking. Moreover, the crayon, when rubbed on a surface, should advantageously provide a relatively uniform laydown, i.e., a relatively smooth and uniform layer of the crayon composition on the surface--without undue flaking. Further, the crayon should provide a mark which is substantially clean, and uniform, in coloration. In addition, the crayon should not be unduly hygroscopic in nature, i.e., it should not absorb water to the extent that it acquires a wet feel and looses mechanical strength.
Obtaining satisfactory levels of performance in regard to all of the foregoing properties has not, however, been a simple matter. On the contrary, such has been found to be problematic when new crayon formulations are developed using components which have not previously been included together in a crayon composition.
Thus, one of the objects of the present invention is to provide a marking composition, e.g., a crayon, which possesses an enhanced level of special effects.
A further object of the present invention is to provide a special effects marking composition which is able to provide a high quality mark on a variety of surfaces.
Another object of the present invention is to provide a special effects marking composition which possesses good mechanical strength.
Yet another object of the present invention is to provide a special effects marking composition which possesses good appearance.
An additional object of the present invention is to provide a special effects marking composition which possesses a relatively low level of hygroscopicity.
A further object of the present invention is to provide a special effects marking composition which possesses a relatively low level of toxicity.
These and other objects and advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.